Set root namespace for Audit::Changes

This change avoids confusion with root namespace of this class on
application boot. An exception is thrown via `bootsnap` when I ran
`bundle exec rails s` or `bundle exec rails c` locally.

`uninitialized constant EE::Audit::Changes (NameError)`

ee/app/services/concerns/approval_rules/updater.rb

@@ -2,7 +2,7 @@
 
 module ApprovalRules
   module Updater
-    include Audit::Changes
+    include ::Audit::Changes
 
     def action
       filter_eligible_users!

ee/app/services/ee/users/update_service.rb

@@ -5,7 +5,7 @@ module EE
     module UpdateService
       extend ::Gitlab::Utils::Override
       include ::Gitlab::Utils::StrongMemoize
-      include Audit::Changes
+      include ::Audit::Changes
 
       attr_reader :group_id_for_saml